[SciPy-User] butter() and filtfilt() - differences between MATLAB and scipy

Fabrice Silva silva@lma.cnrs-mrs...
Fri Jun 28 06:18:12 CDT 2013

Tristan Strange a écrit :
> In MATLAB [...] b comes out as a matrix containing :
> 2.8109e-15   2.5298e-14   1.0119e-13   2.3612e-13   3.5418e-13   3.5418e-13
> 2.3612e-13   1.0119e-13   2.5298e-14   2.8109e-15
> When done in Python using scipy.signal's butter like so:
> [...] the following warning is issued:
> /usr/lib/python2.7/dist-packages/scipy/signal/filter_design.py:288:
> BadCoefficients: Badly conditioned filter coefficients (numerator): the
> results may be meaningless  "results may be meaningless", BadCoefficients)

You should maybe worry about getting (in matlab) such values for b. All
are pretty close to 0. This is what scipy implementation is warning you
about ("Badly conditioned filter coefficients (numerator): the results
may be meaningless"). Using this b vector may lead to output signals
prone to numerical noise...

More information about the SciPy-User mailing list